[RTTY] Skew dancing(Re: Skimmer spots dropped at VE7CC cluster node)

[Pete Smith N4ZR]

Hello, Dai.  The way the RBN is supposed to work is this: There is a 
relatively small group of Skimmers that are known to use highly accurate 
frequency standards - typically GPS-disciplined oscillators - which are 
designated as primary standard stations for skew comparisons.  but 
because HF propagation won't permit any small number of standards to be 
used worldwide, the system also designates Skimmers on each band that 
are agreeing with the primary standards, as temporary standards of 
comparison for a short period of time.  This list is constantly changing.

We've noticed this phenomenon of false skew warnings since early in the 
life of the system, but have never been able to track down the cause. 
It's really not a "red card", just an advisory. The data are useful to 
us, because often they do point to Skimmers that are having problems so 
that we can advise the operators on how to improve their calibration. I 
myself get these "phantom" warnings occasionally , but typically they 
appear and arequickly gone.

Is your OCXO GPS-disciplined, or just periodically recalibrated? OK if 
we add yours to our list of standard stations?

73, Pete N4ZR
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On 10/3/2015 9:06 PM, Dai NAGAKURA wrote:
> Dear members de JF2IWL
>
> This talking may not fit on this reflector.
> I read interesting Lee's busted callsign data as one of RTTY Skimmer.
>
> Then,, How is " Frequensy Busted spots" ?
> I was issued a red card by aggregator many times in WW RTTY
> " your sdr skews 0.7kHz  on 15m "
> But my QS1R with OCXO(0.5ppm/10year)
> captures right frequency.all the time.
>
> I call it "Skew Dancing",  It occurs big contests
> Why this phenomenon occurs ?
>
> My spot may be jumbled by inaccurate skimmers.
> I heard that skew of skimers is calculated by some standard skimer.
> but it is not true.
>
> Can these subject be analyzed by actual data like Lee's?
> Hope skimmers calibrate SDR and provide right spots.
>
> Dai JF2IWL
>
>
>
>
>
> On Wed, 30 Sep 2015 19:19:01 -0600 (MDT)
> Lee Sawkins<ve7cc at shaw.ca>  wrote:
>
>> These links may be interesting to some of you. These are the typical rejected spots of any CC Cluster.
>>
>> RTTY skimmer spots are considered valid if spotted by ONE Skimmer. RTTY Skimmers are generally more accurate than CW and there are simply not enough of them to use 2 or more Skimmers to validate them. CW spots are valid if spotted by 2 or more Skimmers.
>>
>> Here is the list of dropped Skimmer spots by the VE7CC-1 cluster.
>> If you connect to the RBN directly, you will receive all these spots as well as the good ones.
>>
>> Many times there are two calls in succession that are dropped for RTTY calls. I am receiving data from both the RBN and DL4RCK for redundancy. Usually they both spot the same RTTY calls.
>>
>> Most columns are self explanatory.
>>
>> The number directly before a skimmer call is a quality number. It is the number of times a call has been detected as correct minus the number of times it is busted. When the number decreases below 5, it is no longer considered valid. If the active call has not been spotted in 12 minutes it is also no longer considered valid. In one place, for 9A1A the quality number is over 2000. This means 9A1A has been spotted over 2000 times on the same frequency!
>> "Sysop added" means I have manually added a call to the list because it is busted all the time and is never good.
>>
>> http://www.bcdxc.org/ve7cc/ccc/Busted-26-Sep-2015.txt  
>> http://www.bcdxc.org/ve7cc/ccc/Busted-27-Sep-2015.txt  
>>
>> Lee
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